The use of mercury-containing button batteries has increased progressively over recent years and such batteries are now used in progressively more applications, for instance in clocks, photographic apparatus, mini-calculators and hearing aids.
The mercury content of this type of battery varies from tenths of a percent up to about 35%. The remainder of the battery is comprised mostly of iron, zinc, nickel and chromium. About 10 ton of such batteries are sold annually in Sweden. A rough estimate with regard to Europe as a whole is about 500 tons.
It is estimated that about 85% of these button batteries are collected as scrap in Sweden. These batteries are taken, together with other small batteries, to a central plant where they are stored for destruction or final dumping. Since there is still no attractive alternative to destruction, large quantities of these batteries remain in storage. Disposal of batteries that have not been destroyed is an expensive process and is, of course, encumbered with rigorous safety requirements. Thus, there is a considerable need for a destruction method which is suitable for application with such mercury-containing waste, particularly when incitement must be found to increase the extent to;which such batteries are collected, so as to prevent these batteries accompanying typical domestic waste and being dumped on waste tips around the country. Batteries that have not been collected as a matter of routine represent a time-fused environmental bomb. In ten or a hundred years from the time of being dumped, mercury is liable to leak from such batteries in an uncontrolled fashion. This latent threat is even more frightening when viewed on a worldwide basis, where the routine collection of mercury-containing batteries is far less organized than in Sweden.
A method of the kind defined in the introduction has been proposed in International Patent Application WO92/10240. According to this method, waste in the form of fluorescent tubes and the like as well as button-type batteries, are melted down to form a glass melt in a closed reactor, with the intention that resultant HgSe will bind chemically to the glass. The glass is then moulded into briquettes which can be dumped in dumps intended therefor. Thus, when practicing this known method, the waste is destroyed and mercury binds to the waste residue, hopefully in a stable form. The residue is still classified as environmentally hazardous waste and must therefore be disposed of as such.
EP-A-0117865 proposes a method and an arrangement for heating waste in the form of button-type batteries in a rotary furnace, wherein an oxidizing gas is delivered to the furnace for combusting burnable material in the waste and for transporting mercury released in the combustion process from the furnace. The process gas is then purified in a separate gas wash. This waste residue must also be considered as environmentally hazardous waste, since there is a danger of mercury remaining in the residue as a result of oxidation or as a result of recondensing in the waste residue. This danger is also found in the above mentioned method in which selenium is supplied to the system, since the method is carried out in a closed reactor with no agitation or gas transportation.
Accordingly, there is a need for a method which will enable mercury-containing waste to be treated in a manner which will prevent unintentional contamination of the waste residue with mercury to the greatest possible extent, and to enable a mercury-free residue to be formed which can be worked-up with respect to any metal values that may be present or can be dumped without needing to treat the residue as environmentally hazardous waste.